<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .bg{background: pink}
        .fg{color: red}
    </style>
</head>
<body>
    <div id="app">
        <strong v-class="className" class="bg">国庆七天乐 天天都快乐</strong>
    </div>
</body>
<script src="MVVM/mvvm.js"></script>
<script src="MVVM/observer.js"></script>
<script src="MVVM/compile.js"></script>
<script src="MVVM/watcher.js"></script>
<script>
    var vm = new MVVM({
        el:"#app",
        data:{
            className:"fg"
        }
    })

    setTimeout(()=>{
        vm.className = ""
    },2000)
</script>
</html>